In the first part of the four-part series we looked at the essential elements you need to know about as it pertains to DJ PA systems. In the second part, we continued laying the groundwork by responding to some typically common newbie questions. Now, we’re ready to look more closely at both major the different parts of any PA system: Amplifiers (“amps”) and speakers.
Today we’ll look in-depth at both, and discuss the crucial matter of speaker placement, before the next time moving on to cables, establishing and sound checking. Now, a PA amplifier is completely different from a hi-fi amplifier. Power amplifiers are made to allow them to manage their maximum power output for an long period of time. They often have serious high temperature sinks and followers built in, that might get worried you as these could appear noisy in the shop.
But believe that you will play before 100 people at a decent volume and trust me: You won’t hear the fans! The very first thing you should look at will be the basic specs of the amplifier, and at which temps it can operate especially. In venues in hotter parts of the world it can get quite hot even in climate managed rooms and you don’t want your amp to die you in such circumstances. So be sure to consider whether the amp you’re taking a look at can operate in such conditions.
Next, I’d always advise to get amps with protecting circuits. Take good care that you get a good amplifier. The most severe thing that can happen is that you get a cheap amplifier that can’t deal with the heat and its own thermal protection maintains eliminating every five minutes. This will drive you crazy, believe me – I know this from experience!
Give a potential amplifier a listen at low volume. Now, if you hear some noise from the followers, that is alright, nevertheless, you should not hear much static from the speakers too. The sound should be clear and flat. Next, play a tune that you know very well and that has a broad spectrum and then arrive the quantity to “as loud as they will enable you to in the shop”. Even at the high volume the sound should be as to the same as at low volumes close, obviously much louder just.
There should not be loss in frequency response. Some cheap PA amplifiers have a tendency to “forget” to amplify the mids when each goes louder, and in the ultimate end your PA may appear like a tin can with a bass drum. That should not happen. As being a test sound I mainly use the WAV file of the THX test audio you listen to in cinemas.
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You can download that all online. Also some rather “chill” music like deep house or Balearic can be revealing. Speakers are of course the ultimate hyperlink in the string. Speakers are crucial as they are the matter that actually changes the electrical signal from your amplifier into moving air, aka sound waves.
Now why am I stressing moving air? Because it’s essential to full recognize that sound is merely waves in the air that are made by moving the environment. Look at this closely, and you begin to realise why speakers are the real way they are. First thing to understand is that the higher the frequency – up to 20,000Hz (20kHz) is the hearing range – the shorter its wavelength, which means a smaller driver will be sufficient to move the air loud enough. A small driver is needed as a large driver would be simply too slow also. However, the science doesn’t stop there.
In addition, the cupboard (aka the case) plays a serious role in this, as the driver’s membrane isn’t just moving air when it goes out, but also inside the cupboard. That is especially important with bass speakers and subwoofers again. They are able to include porting in the cabinet (bass reflex) to go air from the cabinet, and the within of the speakers can be designed like wind tunnels to move the right amount of air. One interesting point to be aware is that for noises below about 100Hz, you are unable to determine where the sound is via.
That’s why there’s no need for stereo with subwoofers – and just why typical computer gaming speakers (and some small PAs) have two middle/top audio speakers but only 1 “subwoofer”. That was a great deal of information Now. So practically, what does it mean for you when you’re making your buying choices? Really, it’s just important to remember that there are no miracles in the wonderful world of speakers.